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C E Smith

Publications and source records attributed to C E Smith.

At least 307 records · Page 17Linked to original sources
PubMed1977

Quantitative analysis of cell turnover in the enamel organ of the rat incisor. Evidence for ameloblast death immediately after enamel matrix secretion.

During renewal of the enamel organ in the rat incisor cohorts of epithelial cells are transported sequentially through presecretory, secretory and maturation zones to the gingival margin where the life cycles of these cells terminate. This process was examined kinetically by determining the absolute flux of cells within each of these zones of amelogenesis. It was found that the efflux of ameloblasts, stratum intermedium and papillary layer cells from the presecretory zone was about equal to the efflux plus expected growth within the secretory zone. However, between the secretory and maturation zones about 50% more ameloblasts entered the maturation zone than were required to account for the egress at the gingival margin and the expected growth. Since there was no similar imbalance between these zones for papillary layer cells, it was concluded that this discrepancy must represent a 50% reduction in the size of the ameloblast population during the maturation stage of amelogenesis. It was calculated that a little over 25% of the loss occurred immediately at the start of maturation within the region of postsecretory transition and the remaining 25% of the loss occurred throughout the subsequent regions of the maturation zone. In addition to the kinetic analysis graphic reconstructions, or surface maps, of ameloblast nuclei were prepared. These maps illustrated the characteristics of ameloblast nuclear packing within the three zones of amelogenesis and they provided quantitative confirmation that as ameloblasts progress through the maturation zone, there is a loss of cells in an amount predicted by the kinetic analysis.

Ameloblasts↗
PubMed1977

Multinucleate ameloblasts in the rat incisor.

Cytological examination of the rat incisor enamel organ with the light and electron microscope revealed a small number of ameloblasts which contained two and sometimes three or more nuclei per cell. A multinucleate ameloblast usually contained two vertically apposed nuclei situated near the base of the cell. A narrow cytoplasmic band was interposed between adjacent nuclear envelopes. The apical nucleus was often the more elongated of the two nuclei and it fitted a convexity or a concavity within the more basally positioned nucleus. In serial sections examined with the electron microscope no connections were observed between the nuclei. In animals injected with 3H-thymidine instances of multinucleate ameloblasts were found within the advancing front of labeling where only one of the nuclei contained label. Finally, quantitative analysis by nuclear counting established that multinucleate ameloblasts were 60 times more frequent within the maturation zone as in the secretory zone of amelogenesis. As well, the numbers of multinucleate ameloblasts increased progressively in the course of the maturation stage. It was concluded that multinucleate ameloblasts increase with cell age and likely arise by the process of cell fusion.

Ameloblasts↗
PubMed1977

Inorganic trimetaphosphatase as a histochemical marker for lysosomes in light and electron microscopy.

A new cytochemical method is presented for the light and electron microscopic localization of lysosomes in mineralized and soft tissues. Inorganic trimetaphosphate is used as substrate in a lead chelate incubation medium at pH 3.9. Lysosomes in several tissues are strongly reactive, and reaction product is frequently present in Golgi saccules and GERL. The reaction can be differentiated from acid glycerophosphatase activity, is relatively insensitive to fixation and demineralization procedures, and the reaction is often complete after short incubation times.

Animals↗
PubMed1976

Movement of entire cell populations during renewal of the rat incisor as shown by radoioautography after labeling with 3H-thymidine. The concept of a continuously differentiating cross-sectional segment. (With an appendix on the development of the periodontal ligament).

Renewal of the rat incisor was studied in three dimensions by employing a serial cross-sectioning technique to locate the boundary between labeled and unlabeled cells in the enamel organ and odontoblast layer at various times after a single injection of 3H-thymidine. This boundary, or leading edge of the front of labeling, was graphically illustrated through point-plotting reconstruction of the labial surface of the incisor. At one hour after the injection of 3H-thymidine the front of labeled ameloblasts was located within the presecretory zone related to early predentin secretion. This front formed a "C"-shaped curve stretching across the labial surface of the tooth from the lateral to the mesial cemento-enamel junction. The "C" was open anteriorly and the lateral arm extended almost twice as far incisally as the mesial arm. The edge of the front of labeled odontoblasts was positioned apical to and parallel with this "C"-shaped curve. The morphological appearance of all cells along each respective front was found to be similar. As the fronts of labeled ameloblasts and labeled odontoblasts moved forward with the erupting incisor, the cells along these fronts differentiated simultaneously and subsequently formed enamel and dentin. Throughout this movement the distance between fixed points along the leading edge of the front of labeled ameloblasts, and its positional relationship to the front of labeled odontoblasts, did not change appreciably. This indicated that cells of the tooth were being carried incisally at a uniform speed. It was concluded that renewal in the rat incisor consists of the generation by the bulbous part of the odontogenic organ of epithelial "U"-shaped cross-sectional segments which enclose a core of pulp. As this segment is transported towards the gingival margin, cellular differentiation and subsequent formation of hard tissue is seen to begin at the central labial side of the segment and to progress in a mesial and lateral direction towards the lingual side. In the process, the limits of the enamel organ at the mesial and lateral cemento-enamel junctions are established and the entire circumference of the segment is eventually enclosed by a rim of dentin.

Ameloblasts↗
PubMed1976

Arbovirus infections in Sarawak: the role of the domestic pig.

The possible role of pigs as arbovirus maintenance hosts and their importance as amplifier hosts was studied. Blood samples from 464 pigs of all ages collected in 1962 and 1964 were tested against 10 arboviruses. Antibodies to Japanese encephalitis and Getah viruses were particularly prevalent and their calculated monthly infection rates were 19-5% and 13-3% respectively. In 1969, 447 pigs were bled monthly throughout the year and the infection rates for Japanese encephalitis virus were calculated in pigs during the first year of life. Infection rates were not uniform throughout the year; the rate increases as the pig grew older and there was a marked seasonal increase in the infection rate in the period from November to January. This coincided with the seasonal major population peak of Culex tritaeniorhynchus following intense breeding of this mosquito prior to rice planting. It is suggested that, in Sarawak, the pig acts as a maintenance host of Japanese encephalitis in a cycle involving C. gelidus mosquitoes and also acts as an important amplifier host towards the end of the year in a cycle involving C. tritaeniorhynchus. It is further suggested that Getah virus is maintained in a similar cycle between C. tritaeniorhynchus and pigs.

Age Factors↗
PubMed1976

Comparative susceptibility of Atlantic salmon (Salmo salar) to the enteric redmouth bacterium and Aeromonas salmonicida.

The bacterium causing enteric redmouth (ERM) and Aeromonas salmonicida were found to be equally pathogenic for fingerling Atlantic salmon (Salmo salar). Injection of 5 x 10(5) cells of ERM or A. salmonicida killed all salmon within 96 h. After a 30 min exposure to water-borne cells of the two test bacteria about one-half of the test salmon died within 14 days. Both ERM and A. salmonicida were transmitted horizontally. Results indicate that efforts should be made to prevent introduction of ERM into watersheds where Atlantic salmon occur.

Aeromonas salmonicida↗
PubMed1975

Mechanics of chromatin template activation. Physical evidence for destabilization of nucleoproteins by polyanions.

Thermal denaturation profiles were used to quantitate the destabilizing activity of five classes of polyanions in an effort to explain previously reported differences in activity among apparently similar polymers. This physical assay for polyanion action on chromatin is free of the biochemical complications associated with template assay systems. Most polyanions tested caused a thermal destabilization of the normal nucleohistone complexes of rat thymus chromatin and exposed free or weakly complexed DNA. Polyphosphates dissociated chromatin even when their net charge was as low as 6, and activity per unit of weight increased with chain length only for polymers containing less than about 20 phosphate units; pyrophosphate was inactive. Two polymers which had no influence on chromatin had a low negative charge density. Some, such as polycytidlate and denatured DNA, possessed a high charge but caused only minor changes in the shape of denaturation profiles and exposed little or no free DNA. The highly active nucleic acids, ribosomal RNA and polyguanylate, were distinguishable from inactive nucleic acids by having more secondary structure and potentially less steric hindrance for anionic interaction with chromatin. There was evidence that some polyanions dissociate certain histones before others. Although data obtained show that some histones may be redistributed from chromatin onto added double-stranded DNA in a medium containing urea, this does not appear to interfere significantly with the interpretation of typical thermal denaturation profiles of chromatin.

Animals↗
PubMed1975

Histological and three dimensional organization of the odontogenic organ in the lower incisor of 100 gram rats.

A three dimensional reconstruction of the epithelial tissue at the apical end of the lower rat incisor was made from serial 1 mum thick cross sections. This tissue formed an elongated structure, called the odontogenic organ, which was composed of a bulbous and a "U"-shaped part. Both parts were joined to one another at the posterior aspect of the apical foramen. The bulbous part of the odontogenic organ was situated at the lingual side of the "U"-shaped part and protruded anteriorly over the pulp. It was formed by cells of the outer dental epithelium and stellate reticulum whose organization suggested that the bulbous part was important in the production of cells for renewal of all the epithelia of the incisor. The "U"-shaped part of the odontogenic organ was apparently derived from the bulbous part and delineated the pulp by forming the lateral, mesial and labial sidewalls around the apical foramen. It was composed of all the epithelial cell types recognizable as precursors to (a) cells of the enamel organ which form the enamel, and (b) Hertwig's epithelial root sheath, a part of the odontogenic organ which induces the formation of dentin on the lingual aspect of the incisor.

Ameloblasts↗
PubMed1975

Histological and three dimensional organization of the odontogenic organ in the upper incisor of 100 gm rats: comparison with the lower incisor.

The epithelial tissue forming the posterior aspect of the apical foramen in the upper incisor of the rat was reconstructed from 1 mum thick serial cross sections. Like the lower incisor, this portion of the odontogenic organ in the upper incisor was composed of a bulbous and a "U"-shaped part. However, the bulbous part was considerably blunter and the "U"-shaped part much larger in circumference in comparison to the lower incisor. Although no differences were found between the upper and lower incisor regarding the contents and the basic organization of cells within each part of the odontogenic organ, specific differences were found within the bulbous part in the upper incisor. There was a more definitive boundary between the outer dental epithelium and stellate reticulum, a more intimate relationship of cell streams to the stellate reticulum, and a noticeable lack of swirling of cells as part of the streams. These features suggest that the activity inside the bulbous part is less intense in the upper incisor than it is in the lower incisor. In addition, the relationships between the bulbous part, the "U"-shaped part and the root sheath part of the odontogenic organ and the enamel organ were described for the upper incisor.

Ameloblasts↗
PubMed1975

Cellular renewal in the enamel organ and the odontoblast layer of the rat incisor as followed by radioautography using 3H-thymidine.

Renewal of the cell populations of the incisor was studied in 100 gm male rats injected with a single dose of 3H-thymidine and sacrificed at various times from one hour to 32 days after injection. Radioautographs showed that a cohort of labeled cells within the enamel organ, odontoblast layer, and pulp was carried passively with the erupting incisor from the apical end towards the gingival margin where the life cycle of these cells was terminated. Labeled cells in the upper and lower incisor, although traversing different absolute lengths, were found in approximately the same functional stage of their life cycle at similar times after the injection. Thus, by one and on-half days labeled ameloblasts began inner enamel secretion and, by eight days (upper) or nine days (lower), complement outer enamel secretion. By 32 days labeled ameloblasts had traversed the entire enamel maturation zone and were located at the gingival margin. Labeled odontoblasts followed closely the movement of labeled ameloblasts. The mean rate of ameloblast migration was 567 mum/day on the upper incisor and 651 mim/day on the lower. For the odontoblasts this rate was 55 mum/day (upper) and 631 mum/day (lower). Finally, it was found that as the rat age, the duration of the life cycle for epithelial and pulp cell populations of the incisor increased because of growth within the lonitudinal axis of the tooth. It was concluded that the apical end of the incisor literally "grows backward" in the bony socket, and hence, the duration of the life cycle becomes greater simply because it takes cells longer to physically reach the gingival margin.

Ameloblasts↗
PubMed1975

The significance of mosquito longevity and blood-feeding behaviour in the dynamics of arbovirus infections.

Mosquito longevity and blood-feeding behaviour are very important but neglected factors in the dynamics of arbovirus infections as changes in them affect transmission rates exponentially. Some mosquito species feed on a narrow range of vertebrates, some on a wide range, both influenced by host-availability and other environmental and behavioural factors. Only those which feed on maintenance hosts contribute to maintenance of the infection. Some species change their feeding pattern with season. The frequency of blood-feeding depends inter alia on environmental temperature. Longevity is perhaps most important: the majority of mosquitoes infected probably do not survive long enough to become infective; it is influenced by relative humidity, temperature and predation. Longevity, feeding frequency and the extrinsic incubation period are all temperature dependent and are therefore important rate determinants in seasonal epizootics or epidemics. Equally, their relative stability in the tropics contributes to the equilibrium of an enzootic or endemic.

Aedes↗